1. Field of the Invention
This invention relates to achieving more energy-efficient horizontal motion of a two-member knuckle boom, especially but not necessarily those which carry a tree-handling tool at the distal end thereof. The term “tree-handling tool” throughout this specification is intended to encompass, for example, tree felling; tree limbing heads; tree processing heads; wood-handling grapples for piling or loading trees or logs; and other such tools in the tree-harvesting industry.
2. Description of the Prior Art
A typical two-member knuckle boom comprises a hoist boom having a proximal end pivoted to the machine base, and a stick boom having a proximal end pivoted to the distal end of the hoist boom. In the tree-harvesting industry, a tree-handling tool such as grapple tongs would be mounted on the distal end of the stick boom. A hoist cylinder is mounted between the machine base and the hoist boom, and a stick cylinder is mounted between the hoist boom and the stick boom.
The invention expands on the concepts described and claimed in Canadian patent no. 2,317,670, granted Jul. 16, 2002, and in corresponding U.S. Pat. No. 6,443,196, granted Sep. 3, 2002 (hereinafter referred to as “the prior Kurelek patents”). The prior Kurelek patents explained the concept of a hydraulic circuit for a knuckle boom which provides connecting hydraulic lines between the working ends of the hoist and stick cylinders providing an oil flow so as to enable shunting of hydraulic oil between the cylinder working ends. When these cylinders are alternately extending and contracting during reaching actions with the tool carrying knuckle boom, such as is always a part of tree harvesting, the circuit in that invention shunts load supporting hydraulic oil between the cylinders rather than dumping it to tank as with previous conventional circuits. This has resulted in reduced working horsepower, i.e. fuel used and heat generation, and the ability of the operator to do reaching and tucking by operating just one lever, while continuing to do lifting and lowering with the other. This is explained in detail in the prior Kurelek patents.
In the prior Kurelek patents, there is no direct control of the shunting of hydraulic oil, for example via a valve or pump. Instead, the “reach” movement of the boom (i.e. generally horizontal extension or retraction) is controlled by an additional hydraulic cylinder, acting as a “reach” cylinder, mounted between the hoist and stick booms. In one sense, the reach cylinder in effect controls or constrains the shunting of oil between the working ends, since the reach cylinder determines the relative positions of the hoist and stick cylinders. The reach cylinder operates one of the knuckle boom angles, usually working alongside the stick cylinder, and causes the load supporting oil to flow back and forth between the hoist and stick cylinders. In practice, tree harvesting machines with the concepts of the prior Kurelek patents do function with benefits as described, and have already become well-accepted by users.
The reach cylinder does not normally do major load supporting work but is required to provide the horizontal push and pull forces at the tool. Thus when as described in the prior Kurelek patents, the reach cylinder is located beneath the boom assembly, any push forces needed at the tool when reaching in an outward direction is obtained by pressurizing its base end. Since the base end area of typical modern logging machine cylinders is always about twice their rod end areas this is good for operations where the major knuckle boom function is to intermittently push hard on something under good speed control while reaching out, and to return quickly at light load while tucking back in.
FIG. 1 (prior art) is an example of such a prior invention case. The tree butt is gripped in a holder while the knuckle boom is reaching out to forcefully shear off limbs from the tree bole. After going through one of several options in bucking and placing the limbed tree part the boom must grasp and advance the next length of unlimbed tree so that it can be gripped by the holder for the next limbing stroke. Advancing the unlimbed tree with reach-in as it slides on the ground is usually much easier than it is to remove limbs on the stroke out, so the reach cylinder configuration and location in the prior Kurelek patents is good (for push type limbing).
The cylinder actions, hydraulic oil flows and operator controls, including the limbing-head-to-tree alignment, are taught in the prior Kurelek patents.
However, it has been realized by the inventor that there are applications of the efficient reach principle that would rather have the powerful steady stroke direction be when tucking in, rather than when reaching out.
FIG. 2 (prior art) depicts a logging operation that is often used in tree harvesting. Another illustration can be seen in Hamby, U.S. Pat. No. 4,899,794, FIG. 1. In this case the knuckle boom machine is basically a loader and has a grapple as the tool at the end of the stick. When limbing is wanted the loader at near full reach inserts the tree into a stationary limbing head and pulls it towards itself. Limbs are thus removed by a combined action of the conventional knuckle boom and swinging of the upper, as hydraulic oil is typically wastefully pumped into the base of the hoist cylinder and into the rod end of the stick cylinder. Davidson U.S. Pat. No. 5,406,997 FIG. 1 also shows a loader doing “pull-through” limbing apparently with swing action. It is obvious though that if only swinging is used there is much tail sweep of the tree so reaching in and out is usually also used. After disposing of the limbed and bucked log the grapple must race out empty, but still wastefully, to grasp the butt of the next bole to be limbed.
If the tool being used on the knuckle boom end is one that severs the tree off the stump at an extended reach then sometimes it is wanted (e.g. for processing) to forcefully drag the tree in closer to the machine against the resistance of ground friction or incidental limb contacts. The operator can well give up reach force in the extending direction when the empty head is carried above the ground and avoiding other tree stems, and instead get more pulling force.
In converting a knuckle boom to be more efficient according to the prior Kurelek patents we do achieve the efficient reach objective. Pressurized oil is exchanged between the stick and hoist cylinders during pulling in and reaching out. But the slower, higher force action of the extending reach cylinder would occur when going back with empty tongs to get the next bole and not when hard pulling might be wanted to remove limbs or extract an entangled felled tree: The quicker less forceful action of the rod end area would attempt to do the limbing (pulling) stroke. The operator would appreciate the ease of one hand operation and the generally faster reach speeds but unless major changes in pressures and cylinder sizes were made he would probably wish for more pulling force.